Lathrocasis tenerrima

Introduction

Lathrocasis tenerrima is a small, delicate, annual plant that is easily overlooked in nature. This species is tetraploid (i.e., it has four sets of chromosomes, with nine in each set), self-pollinating, and occurs at mid elevations (1500-2750 meters) in the Great Basin and Rocky Mountain regions of the Western United States. This species represents an interesting phylogenetic lineage that diverged early in the evolution of tribe Gilieae, yet either has not radiated like the species-rich and closely related Gilia, and Allophyllum+Collomia+Navarretia clades, or has lost any close relatives through extinction. The name Lathrocasis is derived from the Greek lathro- (= hidden, secret) and kasis (= sister), and was coined because the relationships of this species have been obscure; tenerrima is derived from the Latin tener, which means delicate or soft, in reference to the fine, threadlike pedicels of this species (Johnson and Weese, 2000).

Lathrocasis tenerrima is distinguished from other Polemoniaceae by a combination of characters (Johnson and Weese, 2000; Johnson et al., 2004). These include the mostly entire leaves, widely diverging branches with threadlike pedicels that angle 90 degrees or more from the stem, being uniformly covered with short, gland-tipped hairs, minute funnelform flowers with a simple veination pattern, stamens equally inserted approximately mid-tube, one seed in each fruit chamber (three seeds per fruit), and seeds with a warty covering that produces mucilaginous (sticky) threads when wet.

This species is easily identified by paying attention to the details of its features. Its flowers are very small, however, so a hand lens or other means of magnification are essential to study the plant. Some written descriptions for the species are misleading. For example, the flowers have been described as campanulate (cup-shaped) and the calyx tube being split more than half way to the base (i.e., lobes longer than the tube); Its glands and pollen grains have also been mischaracterized. Among Polemoniaceae, this species is most likely to be confused with Aliciella micromeria, which is also small flowered and has a similar overall appearance with very fine branches and diverging flower stalks. Aliciella micromeria, however, usually has several lobes on each side of its leaves, lacks chloroplasts in its glands, and has seeds that lack warts (having well defined cell wall boundaries instead) and do not become sticky when wet.

Geographic Distribution

Lathrocasis tenerrima is distributed in parts of the Great Basin and Rocky Mountain floristic provinces of western United States. Its range extends north from California, Nevada, Utah, and Colorado into Oregon, Idaho, Wyoming, and Montana and from Wyoming west to the Cascades of Oregon and the Sweetwater Mountains of Mono County, California. Though the type specimen (the original collection the species is named from) is listed as being from "Utah", it was collected in 1869 when the Utah territory included parts of what is now Wyoming, and it most likely was collected in what is now that state (Johnson and Weese, 2000).

Phylogenetic Relationships

Lathrocasis tenerrima has been allied with numerous species over the years, but seemingly as an afterthought rather than due to direct study of this species. Chloroplast DNA sequences provided the first firm evidence suggesting L. tenerrima be removed from the genus Gilia (Johnson and Soltis, 1995). Subsequent studies of morphology and further DNA sequence analysis further support removing this speceis from Gilia, but are not strong in anchoring this genus to a single sister group (Johnson and Weese, 2000; Johnson et al. 2004, 2008). Lathrocasis is either sister to Gilia, to a clade composed of Allophyllum, Collomia, and Navarretia, or to both of these groups combined.

References

Grant, V., and A.G. Day. 1998 [1999]. Transfer of some species from Gilia to Allophyllum and Tintinabulum, and the effects of the transfer on the generic definition of Gilia (Polemoniaceae). Phytologia 84:368–382.

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Lathrocasis tenerrima.
Authored by
Leigh Johnson.
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